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Abstract:

Provided are an in-mold degassing structure, which acts by using no
external control means, and a mold having that structure. The degassing
structure comprises a sliding member (10) for receiving the pushing force
of an elastic member from the bottom side, and a sliding member acceptor
(20) for accepting the sliding member (10) slidably in the vertical
direction. The sliding member (10) includes a vertical bottomed hole (12)
communicating with a mold cavity and at least one side opening (13)
communicating with the vertical bottom hole and opened to the side face.
The sliding member acceptor (20) includes degassing ports (21)
communicating in an initial state with the side opening (13) of the
sliding member and closed when the sliding member is slid in a direction
against the elastic member by the flow tip portion of the molten
material. The degassing structure is mounted in the molten material flow
passage or in the cavity near the trailing end of the molten material
flow passage, thereby to degas the mold inside.

Claims:

1. An in-mold gas vent structure, comprising:a sliding member that
receives, from an opposite side, an impelling force exerted by an elastic
member and that includes a bottomed hole, formed in a direction in which
a molten material flows, and at least one side opening, communicating
with the bottomed hole and being open in a direction transecting the
direction in which the molten material flows; anda sliding member
acceptor that slidably accepts the sliding member in a direction parallel
to the direction in which the molten material flows, and that includes a
gas vent port, which communicates with the side opening of the sliding
member in the initial state, in which there is no pressure influence
resulting from the flow of molten material, and is closed when the
sliding member is thereafter impelled inward, compressing the elastic
member, by the leading end of the molten material,characterized by being
suitable for being mounted in a space defined by a cavity plate and a
core plate, or along a molten material flow passage connected to the
space, or near the trailing end thereof.

2. The in-mold gas vent structure according to claim 1, characterized in
that the elastic member, for impelling the sliding member toward the
opposite side, is provided as either one component, or an assembly of
components, selected from a helical spring, a leaf spring, a rubber-like
elastic member, or a fluid pressure actuator.

3. The in-mold gas vent structure according to claim 1 or 2, characterized
by including a plurality of sets, each consisting of the side opening,
formed in the sliding member, and the gas vent port, formed in the
sliding member acceptor.

4. The in-mold gas vent structure according to claim 1 or 2, characterized
in that gas vent effects using the gas vent ports are changeable in
accordance with viscosity of the molten material.

5. The in-mold gas vent structure according to claim 4, characterized in
that at least either the gas vent ports or the side openings are employed
as non-linear gas release passages.

6. The in-mold gas vent structure according to claim 4, characterized in
that the gas vent ports and the side openings define opening areas, so
that the cross-sectional size for the opening areas changes, over time,
in accordance with distances the sliding member moves.

7. The in-mold gas vent structure according to claim 1 or 2, characterized
by being suitable for being fitted into a recessed portion formed at a
predetermined location in the mold.

8. A mold characterized in that:a gas vent structure comprisesa sliding
member that receives, from an opposite side, an impelling force exerted
by an elastic member and that includes a bottomed hole, formed in a
direction in which a molten material flows, and at least one side
opening, communicating with the bottomed hole and being open in a
direction transecting the direction in which the molten material flows,
anda sliding member acceptor that slidably accepts the sliding member in
a direction parallel to the direction in which the molten material flows,
and that includes a gas vent port, which communicates with the side
opening of the sliding member in the initial state, in which there is no
pressure influence resulting from the flow of molten material, and is
closed when the sliding member is thereafter impelled inward, compressing
the elastic member, by the leading end of the molten material; andthe gas
vent structure is integrally formed in advance in a space defined by a
cavity plate and a core plate, or along a molten material flow passage
connected to the space or near the trailing end thereof.

9. The mold according to claim 8, characterized by being integrally formed
in advance with the gas vent structure, wherein gas vent effects using
the gas vent ports are changeable in accordance with viscosity of the
molten material.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a gas vent structure, provided for
a mold used for the injection molding of various types of materials, such
as plastics, ceramics, rubber and glasses, or for the die casting of
metals or alloys, according to which, in an internal space (hereinafter
also referred to as a cavity) of a mold filled with a molten material, a
molded product will be less affected by gas generated by the molten
material and residual air in the space, and thus, the external
appearances of the finished product can be improved and the occurrence of
defective products can be reduced. The present invention also relates to
a mold incorporating this structure.

BACKGROUND ART

[0002]A mold provided by pairing a cavity plate and a core plate is
employed for injection molding using various materials, such as a plastic
(synthetic resin), a ceramic, a rubber, a glass and liquid crystal, or
for die casting using a variety of materials, such as aluminum, zinc, tin
and copper. When a molten material, such as plastic or metal, is injected
into an enclosed space (hereinafter also referred to as a cavity), and is
thereafter cooled in a predetermined manner, a finished product having a
desired shape and structure is obtained. Generally, when a plastic, a
ceramic, a rubber, a glass or a metal, that is, a raw material, is heated
until it reaches an appropriate molding condition, a gas consonant with
the material component is generated. The types and amounts of gases
generated differ, depending on the heating temperatures, the material
types, indirect materials to be added, etc., and also differ in
accordance with mold cavity volumes.

[0003]Fine finishing is performed for the mold cavity, to improve the
surface property and the external appearance of a finished product, and
is also performed for the contact surfaces of the cavity plate and the
core plate to ensure an airtight plate juncture. An elastic packing may
also be positioned between the cavity and core plates, at their contact
surfaces, to more simply provide an airtight juncture. Within the
airtight mold cavity, gas components, such as those generated by a molten
material and residual air, are present, as previously described. These
gas components, which failed to be exhausted by an impelling force when a
molten material was injected, prevent the molten material from spreading
throughout the interior of the cavity, so that molding failures, such as
short shots or surface irregularities, tend to occur. Further, when there
is a gap in the juncture between the plate contact surfaces that permits
gas components to be freely exhausted from the mold cavity, the molten
material could enter the gap and create mold flashing or blowholes
(unevenness) on the surface of the molded product, thereby degrading the
product quality.

[0004]According to patent document 1, which is conventional art that
provides, for the removal of the adverse affects of gas enclosed in the
mold cavity, a gas vent path 11 that communicates with a gas vent hole
10, formed near the distal end of the mold cavity. A structure disclosed
releases gas by opening and closing, using a slidable core member 12, the
portion that connects the gas vent hole 10 and the gas vent path 11. In
this case, a timer and another control mechanism are employed to
selectively open and close the channel using the core member 12. The
operating timing is determined based on the setup of a controller that is
selected while taking into account the flow state of a molten material
and other relevant conditions.

[0005]However, the flow state of a molten resin greatly differs,
depending, for example, on the type of thermoplastic resin that is used
as the molding material, the use of either a single resin or an alloy
prepared by mixing a plurality of resins, the mold structure, the size of
a finished product, the structure of the mold cavity, and whether or not
an insert is used. For determining the setups for the timer and the other
control means, the repetitious employment of trial and error is required
by actually flowing molten resin, and this process imposes a greater load
on operators responsible for molding to prevent the occurrence of
defects. Further, when employing in die casting a specific type of metal
or alloy, since the flow velocity of a molten material is remarkably high
because of its low viscosity, adequate control for opening and closing of
the channel is difficult.

[0006]Patent document 2 discloses that slide slots are formed from the
surface of a cavity to the inside of a mold, and that a moving member is
provided that is movable along the slide slots in the axial direction to
form a gas release groove. The objective is the opening and closing of
gas passage means that employs the forward or backward movement of the
moving member, which occurs upon the contact of the leading end of a
molten resin, to permit communication between the interior and exterior
of the cavity via the gas release groove. However, detailed machining of
a mold is requisite, and machining, maintenance, checking, repairing,
etc., for the mold are complicated.

[0007]Patent document 3 discloses a structure wherein a gas vent valve is
provided near the resin injecting portion at the bottom end of a cavity,
and wherein, at the initial processing time, the gas vent valve 7 is
opened and gas is released, and subsequently, when a pressure sensor
located near a gate has detected a pressure rise in the resin, the gas
vent valve is closed. According to this conventional art, in the initial
period for injecting the molten resin, the gas vent valve is open, and
when the pressure is increased in association with the flow state of the
resin, the gas vent valve is closed to prevent leakage of the molten
resin. However, for this conventional art, as well as for patent document
1, control means for opening or closing the gas vent valve, based on
signals received from the pressure sensor, is additionally required.

[0008]Patent Document 1: JP-A-9-277310

[0009]Patent Document 2: JP-A-2000-15668

[0010]Patent Document 3: JP-A-2003-170479

SUMMARY OF INVENTION

Technical Problem

[0011]Objectives of the present invention are to provide a gas vent
structure, used for the internal space of a mold, that is automatically
actuated, without external control means being required, by receiving an
impelling force from the leading end of a molten material that is flowing
inside the mold, and to provide a mold that includes this gas vent
structure. It should be noted that a mold employed for the present
invention is not limited to a mold used for the injection molding of
various types of plastic (synthetic resins), but includes a mold used for
the injection into a space (cavity) of molten materials, such as ceramic,
rubber, glass or liquid crystal materials, and a mold used for the die
casting of various types of metals, such as aluminum, zinc, tin and
copper.

Solution to Problem

[0012]The present invention according to claim 1 is an in-mold gas vent
structure, comprising: [0013]a sliding member 10 that receives, from an
opposite side, an impelling force exerted by an elastic member and that
includes a bottomed hole 12, formed in a direction in which a molten
material flows, and at least one side opening 13, communicating with the
bottomed hole and being open in a direction transecting the direction in
which the molten material flows; and [0014]a sliding member acceptor 20
that slidably accepts the sliding member 10 in a direction parallel to
the direction in which the molten material flows, and that includes a gas
vent port 21, which communicates with the side opening 13 of the sliding
member in the initial state, in which there is no pressure influence
resulting from the flow of molten material, and is closed when the
sliding member 10 is thereafter impelled inward, compressing the elastic
member 14, by the leading end of the molten material, [0015]characterized
by being suitable for being mounted in a space defined by a cavity plate
and a core plate, or along a molten material flow passage connected to
the space, or near the trailing end thereof.

[0016]The present invention according to claim 2 is the in-mold gas vent
structure characterized in that the elastic member 14, for impelling the
sliding member 10 toward the opposite side, is provided as either one
component, or an assembly of components, selected from a helical spring,
a leaf spring, a rubber-like elastic member, a fluid pressure actuator,
etc.

[0017]The present invention according to claim 3 is the in-mold gas vent
structure for claim 1, characterized by including a plurality of sets,
each consisting of the side opening 13, formed in the sliding member 10,
and the gas vent port 21, formed in the sliding member acceptor 20.

[0018]The present invention according to claim 4 is the in-mold gas vent
structure characterized in that gas vent effects using the gas vent ports
21 are changeable in accordance with viscosity of the molten material.

[0019]The present invention according to claim 5 is the in-mold gas vent
structure characterized in that at least either the gas vent ports 21 or
the side openings 13 are employed as non-linear gas release passages.

[0020]The present invention according to claim 6 is the in-mold gas vent
structure characterized in that the gas vent ports 21 and the side
openings 13 define opening areas, so that the cross-sectional size for
the opening areas changes, over time, in accordance with distances the
sliding member moves.

[0021]The present invention according to claim 7 is the in-mold gas vent
structure characterized by being suitable for being fitted into a
recessed portion formed at a predetermined location in the mold.

[0022]The present invention according to claim 8 is a mold characterized
in that: [0023]a gas vent structure comprises [0024]a sliding member 10
that receives, from an opposite side, an impelling force exerted by an
elastic member and that includes a bottomed hole 12, formed in a
direction in which a molten material flows, and at least one side opening
13, communicating with the bottomed hole and being open in a direction
transecting the direction in which the molten material flows, and [0025]a
sliding member acceptor 20 that slidably accepts the sliding member 10 in
a direction parallel to the direction in which the molten material flows,
and that includes a gas vent port 21, which communicates with the side
opening 13 of the sliding member in the initial state, in which there is
no pressure influence resulting from the flow of molten material, and is
closed when the sliding member 10 is thereafter impelled inward,
compressing the elastic member 14, by the leading end of the molten
material; and [0026]the gas vent structure is integrally formed in
advance in a space defined by a cavity plate and a core plate, or along a
molten material flow passage connected to the space or near the trailing
end thereof.

[0027]The present invention according to claim 9 is the mold characterized
by being integrally formed in advance with the gas vent structure,
wherein gas vent effects using the gas vent ports 21 are changeable in
accordance with viscosity of the molten material. In this case, at least
either the gas vent port 21 or the side opening 13 is employed as a
non-linear gas release passage, and the gas vent port 21 and the side
opening 13 define an opening area, so that the cross-sectional size of
the opening area can be changed, over time, in accordance with distances
the sliding member moves.

Advantageous Effects of Invention

[0028]The in-mold gas vent structure of the present invention is mounted
in a mold that is indispensable for injection molding, die casting, etc.,
and at a location, along a molten material flow passage extended farther
from a gate, or near the trailing end of the passage, on which the
leading end of the molten material exerts the impelling force. For
determination of a specific mounting location, mold flow analysis using a
computer can be performed. The gas vent structure includes: the sliding
member 10, which is to be moved by the impelling force applied by the
leading end of the molten material flow; and the sliding member acceptor
20, which is equipped with the elastic member 14 that exerts force
against the sliding member, from the side opposite, in a direction
towards the leading end of the molten material flow. The bottomed hole
(vertical bottomed hole) 12 is formed in the front face of the sliding
member that contacts the leading end of the molten material flow, and
communicates with at least one of the side openings 13. Before the
leading end of the molten material flow begins to impel the sliding
member 10, the side openings 13 communicate with the gas vent ports 21
that are formed in the sliding member acceptor 20, thereby freely
releasing gas in the cavity to the outside without any difficulty. When
injecting of the molten material in the cavity is continued, and when the
leading end of the molten material flow impels the sliding member 10,
driving the sliding member against the elastic member 14, the gas vent
ports 21 are closed, and the flow of the molten material is completely
blocked.

[0029]It is well known that in the mold the flow speed of a molten
material differs greatly, depending on whether the material is a plastic,
a metal or alloy, a ceramic, a rubber, etc. According to the gas vent
structure of the invention, the release of gases is enabled until the
leading end of the molten material approaches the sliding member, and
almost all of the gases will have been released by the time the leading
end of the molten material reaches the sliding member. Therefore, the
sliding member 10 should be forced to move by the leading end of the
molten material flow to prevent the subsequent flow of the molten
material. The flow speed in this case varies; for example, for a low
viscosity metal, such as aluminum or an aluminum alloy, the flow is
rapid, and for a plastic, ceramic, rubber, etc., the flow is
comparatively slow. Further, when a plastic, metal or rubber material is
employed, the passage closing timing differs in accordance with the basic
material and indirect materials to be added, and the usage, the amount of
material required by the size of a product, etc. However, in this
invention, the passage closing timing used for the gas vent structure is
directly determined, based on the effect produced by the leading end of
the flowing, molten material, i.e., by a so-called self-operation .
Therefore, the gas vent structure does not need to be adjusted for use in
consonance with the type of material employed and the configuration and
size of a product, and no artificial or complicated control means, etc.,
is required,

[0030]In the processing, from the start of the injection of the molten
material into the mold cavity until the arrival of the leading end of the
molten material at the gas vent structure, the molten material flow
passage and the size of the internal space are substantially reduced as
the molten material flows in, and accordingly, the gas mixture,
consisting of the residual air and the generated gas, is externally
released without difficulty. Therefore, the injecting of the molten
material, such as a resin or a metal, can continue for the cavity with no
difficulty. Then, when the molten material flow reaches the location
where the gas vent structure is mounted, as previously described, the
side openings 13 of the sliding member 10 and the gas vent ports 21 of
the sliding member acceptor 20 are displaced from each other, and in a
brief time, the molten material flow passage is closed. Thus, leakage of
the molten material can be appropriately prevented. As a result, the
occurrence of product defects, such as short shots, blowholes, mold
flashes, is greatly reduced, and productivity is improved.

[0031]This in-mold gas vent structure can be prepared in advance as a
standard item, having typical overall dimensions. Further, during a mold
fabrication process, a recessed mounting portion can be prepared in a
mold at a predetermined location, and thereafter, the standard item can
be fitted in this mounting portion and secured using screws, for example.
For manufacturing the body of a mold, a process can be separately
performed using a conventional method, except for the formation of the
recessed mounting portion. Then, a gas vent structure of this invention,
of the above described standard type, can be detachably fitted into the
recessed mounting portion that has been prepared. Therefore, since the
gas vent structure can be prepared in advance as a separate unit, and can
be mounted in a mold having a recessed mounting portion, operating
efficiency can be improved, and material costs and the number of
manufacturing steps can be reduced. When the gas vent structure is not
required because of the type and the property of a molten material used
for molding, a dummy (false member) having the same overall dimensions
can be formed and securely mounted in the recessed portion.

[0032]When the manufacture of a new mold is required because, for example,
a product model has been changed, such a detachable gas vent structure as
the structure of this invention can be removed from the old mold and
reused, by being mounted in the recessed mounting portion of a new mold
that was prepared, thereby reducing the required resources, labor and
costs, and increasing the economical effect. Furthermore, for a mold for
which the above described event need not be taken into account and
continuous use for a long time with no alteration is anticipated, the gas
vent structure for the above described arrangement can be integrally
formed with the mold at the beginning.

BRIEF DESCRIPTION OF DRAWINGS

[0033]FIG. 1 is a plan view (A) and an X-X cross-sectional view (B) of an
example structure for an in-mold gas vent structure according to the
present invention.

[0034]FIG. 2 is a plan view of the operating state of the in-mold gas vent
structure according to the present invention.

[0045]A preferred embodiment of the present invention for a gas vent
structure that is detachable from a mold will now be disclosed, while
referring to accompanying drawings. FIG. 1 is a plan view (A) and an X-X
fragmentary cross-sectional view (B) illustrating the preferred
embodiment for the in-mold gas vent structure of the present invention.
As is apparent from diagram (A), the gas vent structure of this invention
includes a sliding member 10 and a sliding member acceptor 20. Since the
gas vent structure of this invention is a vertical type, on the layout of
the drawings, a bottomed hole is represented as a vertical hole and the
direction in which the sliding member is moved is the vertical direction,
as indicated by an up down arrow 15; however, the gas vent structure of
this invention is either a transverse type or an oblique type, the
bottomed hole is directed transversely or obliquely, and the sliding
direction is either the horizontal or the oblique direction. This also
applies for the following direction.

[0046]The upper end of the sliding member 10 is formed to receive gas that
flows from above in the drawing, as indicated by a thick, white arrow,
and the leading end of the molten material that flows in the same
direction. In the upper end of the sliding member 10, a vertical bottomed
hole 12 having a semi-spherical bottom is formed to permit passing of a
gas mixture, consisting of air and generated gas, before the leading end
of a molten resin, etc., approaches the sliding member 10. Furthermore,
at least one side opening 13, for communicating with the bottomed hole
12, is formed at a position a little before the lower end of the bottomed
hole 12. The expressions employed here, such as "vertical" and "upper",
refer merely to the states illustrated in the accompanying drawings, and
do not relate to the positioning and arrangement for actual use. In this
embodiment, the side opening 13 is formed on either side, and in
consonance with the usage and a material employed for injection, only one
or three or more side openings may be formed. Since the vertical bottomed
hole 12 and the side openings 13 are provided inside the sliding member
10, these components are shown by dashed lines.

[0047]The sliding member acceptor 20 has a recessed portion, as shown in
the X-X fragmentary cross-sectional view in FIG. 1(B), in which the
sliding member 10 is held in contact with the right and left faces and
the rearmost face in the diagram (bottom face) to be slidable along a
guide groove, a slip-off prevention frame, etc. (none of them shown). The
space for permitting the further movement of the sliding member 10 is
defined in the portion of the sliding member acceptor 20, below the lower
end of the sliding member 10 shown in the drawing, and an elastic member
14 is arranged in this portion to impel the sliding member 10 upward. For
the elastic member 14, one of either a helical spring, a leaf spring, a
rubber-like elastic member or a fluid pressure actuator, or an assembly
of several of them, can be employed.

[0048]Therefore, in the initial state of the sliding member 10, to which
no external force has been applied, the sliding member 10 is positioned
above by the elastic member 14, as shown in FIG. 1(A), and the side
openings 13 are communicating with gas vent ports 21. It should be noted
that, as indicated by a long dashed double-short dashed line in FIG.
1(B), the sliding member 10 and the sliding member acceptor 20 are parted
along an appropriate plane, and it is desired that one segment be mounted
on the cavity plate side and the other segment be mounted on the core
plate side. As a result, the side openings 13 and the gas vent ports 21
can be formed as grooves by slotting, instead of by piercing. In the
following disclosure, assume that the segment on the cavity plate side
and the segment on the core plate side are aligned to provide one
assembly.

[0049]Referring to the drawings, the gas vent ports 21, which at least
partially engage the side openings 13 of the sliding member 10, are
formed in the sliding member acceptor 20, one on either side, consonant
with the number of the side openings 13 in the sliding member 10. As
described above, the gas vent ports 21 on the individual sides of the
sliding member acceptor 20 communicate with the respective side openings
13 of the sliding member 10 during a period in which the elastic member
14 is impelling the sliding member 10 upward. Therefore, in the process
for injecting a molten material through the nozzle of an injection
molding machine, a die casting machine, etc., various gases, such as
residual air and gases, generated by the molten material, are externally
removed from the cavity through a channel leading from the vertical
bottomed hole 12 of the sliding member and thence to the side openings 13
and the gas vent ports 21 of the sliding member acceptor 20. As a result,
the occurrence is reduced of molding failures, such as short shots, which
tend to occur in cases wherein the presence of gases interrupts the flow
of a molten material, preventing the material from completely reaching
the terminal end of the cavity, the occurrence of degraded products, such
as products that are burned, or the occurrence of blowholes. In the
drawings, the gas vent ports and the side openings are formed on the same
plane; however, the gas vent ports may open upward or downward,
three-dimensionally, and communicate with the side openings.

[0050]FIG. 2 is a drawing illustrating the state wherein the leading end
of a molten material, such as a resin, flowing from the top, as indicated
by an arrow R, has reached the in-mold gas vent structure in FIG. 1. As a
result, the sliding member 10 begins to move downward, as indicated by an
arrow D, and compresses the elastic member 14 located under the lower
face of the sliding member 10, so that the channel open state, for the
side openings 13 of the sliding member 10 and the gas vent ports of the
sliding member acceptor 20, is shifted to the channel closed state.
Therefore, the flow or leakage of the molten material is completely
prevented, and satisfactory injection results can be anticipated. It
should be noted that when the in-mold gas vent structure of this
invention is employed, by being separated into the cavity plate side and
the core plate side, as indicated by a long dashed double-short dashed
line in FIG. 1(B), the number of grooves, formed by slotting for the side
openings 13 and the gas vent ports 21, and the widths and the depths of
the grooves may differ between the cavity plate side and the core plate
side, and the flow resistance can be variously adjusted in accordance
with the properties of molten materials. Further, in FIG. 1(B), the upper
side is defined as the cavity plate side and the lower side is defined as
the core plate side, but these sides may also be reversed.

[0051]When as described above the sliding member 10 is impelled inward,
compressing the elastic member 14, by the leading end of the molten
material, the gas vent ports 21 are closed and the flow of the molten
material is completely blocked. When the molten material is a plastic, a
ceramic or a rubber, the flow speed is comparatively low and outflow of
the material does not occur. However, since a low-viscous metal, such as
aluminum or an aluminum alloy, has a high flow speed, the metal might
flow out with various gases, such as residual air and gases that are
generated by the molten material during the molten material injection
process, which is performed while the side openings 13 and the gas vent
ports 21 are communicating with each other. Therefore, it is preferable
that effects attributable to gas release through the gas vent ports 21 be
changeable in consonance with the viscosity of a molten material.

[0052]When a gas release passage for, at the least, either the gas vent
ports 21 or the side openings 13 is formed in a non-linear shape, such as
a hooked shape or a nearly triangular shape that is tapered forward, the
amount of gas released to the exterior can be controlled, and a
low-viscous molten material having a high flow speed can be prevented
from flowing out. Furthermore, when the gas vent port 21 and the side
opening 13 define an opening area, the cross-sectional size of which
changes over time in consonance with the distance in which the sliding
member 10 is moved, the same effects as described above can be obtained.
The side openings 13 may be openings having different inner diameters,
such as two openings that provide a large flow rate and a small flow
rate, or three openings that provide a large flow rate, a medium flow
rate and a small flow rate. In this case, the openings that communicate
with the gas vent port opposite are changed based on the distance moved
by the sliding member, and, depending on the communication state, a
connection to the exterior is established, i.e., the amount of gas
released is changed over time. Finally, the sliding member reaches the
channel closing area where no opening is available, the gas release
channel is completely closed. The number of openings, their sizes, the
intervals of adjacent openings, etc., can be determined based on molding
conditions, such as heating temperature and dwell time, while taking into
account the viscosity of a molten material, the amount of gas generated,
etc.

[0053]Further, either the gas vent ports 21 or the side openings 13 may
also be provided as multiple openings having different sizes, and with
this structure, the time-transient control for a gas release volume can
be performed, i.e., the cross-sectional size of the actual opening area,
which is determined by the size or the ratio of an opening that is
aligned with an opening on the other side, is changed over time in
accordance with the distance the sliding member 10 is moved with respect
to the sliding member acceptor 20, and the gas release volume is reduced.
The opening size, etc., can be determined by considering the viscosity of
a molten material, the gas that will be generated, etc., included in the
molding conditions for the molten material.

[0054]In this embodiment, gas release or channel closing is controlled by
bringing the side openings 13, along the sliding face of the sliding
member 10, into alignment with, or separated from, the openings of the
gas vent ports 21. However, to control gas release or channel closing, a
round hole having a stepped or tapered interior, for example, may also be
formed in the sliding member, and a round bar may be projected from the
bottom of the sliding member acceptor 20. With this arrangement, in the
initial state of the sliding member 10, since the distal end of the round
bar on the sliding member acceptor 20 is positioned in the largest
diameter portion of the round hole, the gas components freely pass
through. However, when, as shown in FIG. 2, a leading end R of the molten
material flow starts to impel the sliding member 10, the narrow portion
or tapered portion of the round hole of the descending sliding member 10
closely engages the round bar projecting from the sliding member
acceptor, and the channel is closed. With this arrangement, the gas in
the mold is moved in the direction of travel of the sliding member 10,
and is discharged.

[0055]FIG. 3 is a schematic diagram illustrating examples wherein the
in-mold gas vent structure A of this invention is arranged in a mold, and
in the drawing, arrows depicted with continuous lines indicate directions
in which a molten material flows, while arrows depicted with dashed lines
indicate directions in which gas flows. An example in FIG. 3(A) is for
the injection of a molten material from the left end gate, which is a
single gate. This is the simplest structural example, wherein the molten
material moves only in one direction, showing that the gas vent structure
A is arranged near the terminal end in the direction in which the molten
material flows. FIG. 3(B) shows an example wherein the flow of the molten
material branches at a single gate, and moves in two directions, to the
left and right, and the gas vent structure A. is arranged at the
individual terminal ends in the direction of flow of the molten material.
FIG. 3(C) shows an example for the employment of multiple (two) gates
mainly for molding a large product, and showing that one gas vent
structure A is located at the merging point of molten material flows that
enter from a left gate 1 and a right gate 2.

[0056]FIG. 3(D) shows an example wherein a molten material is branched at
a single gate to fill a cavity with a molten material from two
directions. In this example, two gas vent structures A are located, in
the direction in which the molten material flows, at the distal ends
where the molten material flow passage is bent. With this structure,
during a period until the leading ends of the molten material, branched
in two directions, reach the gas vent structures A, the gas components in
the molten material flow passage and in the cavity are impelled and
externally released. When the molten material has a low viscosity and a
high flow speed, high gas release effects can be provided until the
leading ends of the molten material flow strike bottomed holes 12, and
because of the Venturi effect, it can be anticipated that afterwards, the
flow passage and the cavity will be maintained under a low pressure
(negative pressure). As a result, the injection of the material into the
cavity becomes easier, and the molding operation can be satisfactorily
performed. Since the leading ends of the molten material strike the
bottomed holes 12 and move the sliding member 10, the gas vent ports 21
are closed as in the above described embodiment, and the molten material
then fills the cavity.

[0057]As in these specific examples, when the direction of flow of a
molten material injected through a gate is identified, and the gas vent
structure A of the present invention is located at the terminal end of
the flow by, if available, using a mold flow analysis supported by a
computer, a smooth and ideal form of a molten material can be maintained.
Therefore, molding failures can be greatly reduced, and an improvement in
the efficiency of the molding process and reductions in time, materials,
labor and energy can be realized.

INDUSTRIAL APPLICABILITY

[0058]The in-mold gas vent structure of the present invention is a simple
structure that includes a sliding member and a sliding member acceptor,
and appropriately performs self-actuation, with no delay, when the
leading end of the molten material flow reaches the gas vent structure.
According to the in-mold gas vent structure, the sliding member serves as
a sensor that determines an actuating timing, and also as a control
mechanism, thereby performing so-called self-control. Therefore, not only
a sensor for detecting a phenomenon, but also an operation driver, such
as solenoid means or a hydraulic cylinder, for driving valves, is not
required. Thus, the present invention is useful, while taking into
account the materials to be employed, the processing period time and the
manufacturing costs, etc., and further, since processing time lags can
almost be disregarded, molding failures due to gas in cavities can be
greatly reduced.

[0059]As described above, the in-mold gas vent structure of this invention
includes the sliding member, a compression spring serving as an elastic
member and the sliding member acceptor. Therefore, so long as slotting
for the sliding member and the sliding member acceptor, and machining for
the slide portion to ensure smooth sliding, are performed at the initial
precision, gas is released accurately through self-operation and without
any time delay. It should be noted that the accurate positioning for
mounting the gas vent structure in a mold can be determined in accordance
with predetermined conditions, such as the shape and size of a cavity,
the number of gates and a molten material to be employed, and based on a
molten flow analysis supported by a computer.

[0060]Furthermore, according to the present invention, since the in-mold
gas vent structure is available as a separate item, this structure can be
mounted not only in a new mold, but also in a conventional mold that has
been modified by forming a recessed mounting portion at an appropriate
location. Thus, a large increase in the molding efficiency can be
anticipated. And when a gas vent structure is no longer required for a
mold, this mechanism can simply be removed as an individual item, and can
be employed for another mold. Further, for economical reasons and for
production time reasons, the gas vent structure of the present invention,
which can be repetitiously employed, is preferable, especially for a
mold, called a fad mold, that is designed either to follow a current
trend or to satisfy demands for only a short term, because the
fabrication costs for such a mold should be as low as possible.
Furthermore, for continuous use over a long period, a gas vent structure
having the above described structure may be integrally formed with a mold
from the beginning, since economic efficiency is increased in this way.